Cleaning device arranged in front of the inlet to a waterway

ABSTRACT

Excessive oil contamination creates difficulties for water entering waterways. The invention reduces these difficulties by causing the water to flow through three passages on its way to the inlet, the first passage comprising an oil barrier having a net stretching from the surface of the water, preferably down to the bottom of the waterway, the second comprising a filter cloth with a mesh size between 0.2 and 2 mm 2  and the third comprising a filter formed of particles with closed cells which have been perforated.

Sea-water is used for various purposes. In most cases it must be cleanedfrom particles. One example is the considerable discharge of crude oilfrom leaking Iranian production wells. Oil units of various sizesthreaten, for instance, production in desalination installations andpower plants as well as water inlets for pumping down intooil-conducting formations with the object of maintaining the pressure.Coasts where oil production or loading and unloading from ships iscarried out are subjected not only to the risk of shipping accidents,but also to constant oil spills from normal activities.

Scientific literature relating to the behaviour of oil is for the mostpart pragmatic, i.e. it describes oil discharges which have occurred andthe measures, often improvised, taken to combat them. The behaviour ofthe oil is dependent on the chemical composition of the specific oil andwater concerned and on temperature, water movement, etc. In general,part is volatilized, a second part may float on the surface of the waterfor some time, while a third part forms accumulations floating atvarious depths in the water depending on slight alterations in thedensity of the oil and the water. These accumulations are usually washedashore on beaches or sink to the bottom and may remain for many years.If they have settled on the bottom in relatively shallow water, they canbe broken up or set in motion by movements in the water. According tothe present invention oil is combatted in three steps.

The drawing FIGURE illustrates schematically, in longitudinalcross-section, the apparatus for carrying out the three steps of theinvention.

The first protective step comprises oil barriers 10 from which nets 11,12 of varying mesh sizes are suspended so that the lowermost part 14 ofthe net rest on the bottom of inlet 16. The net is provided with a rope18 at the lower end, enabling it to be raised to the surface in the formof a sack with the object of facilitating the removal of oil lumpscaught there. More than one such barrier may be necessary.

Small particles are able to pass through the net or nets and suchparticles may differ in consistency and size depending on thecircumstances mentioned above affecting the accumulation of the oil. Ingeneral, extremely small particles are unlikely to occur at the depthswhere water is drawn in unless extraordinary winds prevail. A filtercloth 20 with sufficiently fine mesh should in most cases be able tocatch particles which have passed through the nets. The mesh size to beused is a question of optimization taking into consideration thebehaviour of the oil in the specific circumstances and the pressure dropwhich can be accepted. Filter cloths with various mesh sizes can be keptin reserve for special situations. Suitable mesh size may vary from 0.2to 2 mm².

The filter is movable in the direction of the arrows so that its lowerpart 22 covers the area of the inlet channels or tubes. Its upper part24 is drawn over a washing device 26 where the filter is cleared fromparticles with the aid of water, steam or compressed air. The part ofthe filter cloth immersed in the water is inclined to facilitateattraction of the particles or is provided with special sweepers.Scrapers may be used before washing. The motion of the cloth is adjustedto the quantity of particles in the water. A filter of this design mayalso collect particles other than oil accumulations.

Should liquid oil or extremely small particles pass through the filtercloth, a third cleaning step may be introduced in the form of a filteras described in Swedish patent application No. 8301243-5, whichcorresponds to U.S. application Ser. No. 673,746, filed Nov. 8, 1984,now U.S. Pat. No. 4,601,825 which discloses a filter for separating oilfrom water including a closed cell polymer foam, in which the cells havebeen perforated.

Such a filter is shown as unit 30 in the drawing FIGURE and includes aninflow wall 32 and an outflow wall 34, which walls may comprise a wirenetting or perforated sheet metal. Water entering the filter unit flowsthrough a plurality of filter cushions 36, each including units of aclosed cell polymer foam in which the cells have been perforated, theunits being encased in a net-like fabric in order to form the cushions.

I claim:
 1. Cleaning device to be placed in front of an inlet to awaterway for filtering oil from water entering the waterway,comprising:(a) a first passage for the water including an oil barriercomprising a net stretching from the surface of the water down to thebottom of the water, said net arranged so as to form a sack when liftedup from the bottom; (b) a second passage for the water including amovable filter cloth having a mesh size between 0.2 and 2 mm² ; and (c)a third passage for the water including a filter formed of particles ofa closed cell foam polymer in which the cells have been perforated.